RFID in harsh environment


Thread Starter

Trevor Easton

I am currently investigating the use of RFID (Transceiver/Transponders) as a means of machine control in a harse environment. (Steam, Water, Heat, Debris). The system will be used to generate position signals for a PLC mounted on a small locomotive. The Antenna will be on the locomotive and transponders in fixed ground locations. Anyone with similar applications/experience on the list?

Kirk S. Hegwood

Look at Pepperl&Fuchs ID systems. They can use microwaves to read/write data to a tag applied to your locomotive. Good distance.

Kirk S. Hegwood
Hegwood Electric Service, Inc.

Michael Griffin

I don't have any experience with this particular application, but I have a Siemens brochure on their RF systems (MOBY). One of their RF product lines is intended for locomotives and other similar outdoor long range applications. The hardware looked rather rugged (at least that's how the picture looked).

I have used several RF systems, but all were small, short range systems for conveyor use, and none of them were Siemens MOBY, so I can't offer any opinion on their particular product. However, it may be worth while checking out the various RF system manufacturers for other similar products.

I don't know if you have had any previous experience with RF systems, but I will base the following comments on the assumption that you
don't. I appologise if as a result I am repeating something which is obvious to you.

From your description, I would assume that you need a read only system. The tags would have unique fixed codes, and you would read them, but
not write to them. The code would tell the locomotive where it is. Read/write tags which use batteries require regular maintenance (they never
seem to last as long as the specs say they should). EEPROM have a limited number of write cycles. There are some newer FRAM systems, but I don't know how well they actually work.

In my own applications with much smaller (and shorter range) systems though, it is important to pay close attention to the following to avoid

a) the alignment and orientation,
b) range,
c) minimum distance between tags and antennas,
d) mounting (proximity to surounding metal) specifications

Don't try to "push the specs". It is better to be a bit conservative. The manufacturer should be able to supply you with detailed application information, including diagrams with the orientation and field "shape".

The minimum distance between tags and antennas is important as they can interfere with one another if they are too close together. This means that more range is not necessarily better. However, if you are reading "on the fly" (while you are moving), then you need to allow for the tag and
antenna to be within range of one another for long enough to complete their operation. If you want to be able to retry a failed operation, then you need to allow time for that as well.

Make sure that whoever is designing the mounting system for the antennas and tags reads the mounting and orientation instructions and
actually follows them, rather than doing whatever is most mechanically convenient. This is not something which you can run a few tests on to see if it works. Improper mounting or orientation tends to cause problems which come and go for no apparent reason. The only way to be sure of avoiding problems is to do the job properly.

There are usually different options for interfacing to a PLC (at least with the systems I am familiar with). These include:
a) parallel (digital I/O)
b) RS-232 (or 422) with a proprietary protocol
c) some sort of "fieldbus" (e.g. Profibus or Devicenet)

Regardless of which system you use, I would recommend writing the interface logic as a re-usable subroutine, if your PLC supports this. I
would also recommend testing it off line with a bench set-up for all the failure modes you can think of.

Option 'a' (parallel I/O) can look fearsomely complicated when you read the manual, but I recently wrote a subroutine to interface a system
with parallel I/O to an S7-224, and it took approximately 6 or 7 rungs of ladder logic for a subroutine which could read any arbitrary number of bytes and store them anywhere in memory. However, these were 6 or 7 very carefully written rungs, so I would allow myself several days to write and test it.

Your system should allow for RF faults (i.e. an improper read or failure to read was detected). In the cases I deal with, these are usually
caused by bad tags (usually the battery died on the read/write tag), but other causes can be cabling, mechanical orientation problems, etc. One brand has a rather poor connector at the antenna which is a source of trouble. Faults often seem to not recur if you retry the operation. When they do recur, some simple hardware troubleshooting is required.

In our applications we can remove the pallet by hand and test the tag with a hand held tag reader. The rest of the RF system can be tested
with a spare tag (manual RF control for diagnostic purposes is usefull here). I am not sure how you would handle this problem with your locomotive system. Make sure your electricians are properly trained on how the system works and how to troubleshoot it. If the RF system is not a mysterious black box to your tradesmen then you will have a lot fewer problems. Make sure that everyone understands to not introduce mechanical modifications which will interfere with the RF field. Good documentation on how the whole RF
system works together would probably help a lot.

Regardless of what I may have said above about problems, I have found RF systems to be quite reliable in our applications. Your application
is of course rather different, but I hope the above information has been of some help.

I assume you are considering using this at your steel mill. If you go ahead with it, I am sure we would be interested in how it turns out.

Michael Griffin
London, Ont. Canada
[email protected]
Debris and water are not a problem w/ P&F id systems. Heat IS a problem, particularly at steam temperatures. The ID tags are susceptible to heat damage.
Temperature is indeed a problem.
We are have done extensive temperature tests with several makes and types. Cycling the tags from 20 degrees C to about 140 degrees C and back repeatedly. We found that the AEG button shaped models are the only ones that survive.


Helge Hornis

The tags John is talking about are rated for normal applications. We (Pepperl-Fuchs) now offer
High Temperature tags that can be used in tough applications over 200 degree C.

Best Regards,